The fall-out from Liverpool's FA Cup exit at Oldham has intensified, with Brendan Rodgers questioning the mental strength of the club's young players, warning their futures could belong in League One and condemning a lightweight performance that made Matt Smith "look like Didier Drogba".

Rodgers' anger had not diminished 24 hours after Liverpool's 3-2 humiliation at Boundary Park and, in a wide-ranging critique that did not bode well for Martin Skrtel, only Joe Allen and Jordan Henderson of the starting line-up were spared blame. The Liverpool manager denied putting his relationship with his young players at risk by renewing criticism of their performance at Oldham and also rejected suggestions that he has failed to address the squad's lack of physicality with his forays into the transfer market. Liverpool hope to add another young talent, the 20-year-old Brazil midfielder Philippe Coutinho, to their squad on Tuesday subject to a work permit hearing in London.

The Liverpool manager selected only three players over 23 in the starting XI for the fourth-round tie – Skrtel, Luis Suárez and Brad Jones – and admits the performance has cast doubt on the quality of the younger group. "You looked at us and some of our young players and Oldham was a rude awakening," he said. "Some have not had that experience of going to the Championship or League One on loan and doing the dirty work. They have been given the opportunity by a manager who believes in young players. They have come in and done well but we don't have world-class young players, I must be clear on that. They have to come in with the intention of working hard with intensity every day.

"Look at Steven Gerrard's impact when he came on, not just his quality but his sheer enthusiasm for the game. Our young players won't have a greater role model to follow and they're in pole position to learn because they're seeing him every single day. If they're bright enough, they'll learn from him and then hopefully they can be here for a long time. If not, they might find themselves playing in League One later on and they'll regret looking at a world-class player every day and not learning."

Rodgers is particularly angry at the manner in which the Latics' striker Smith terrorised Liverpool's defenders while scoring his first two goals for the club at Boundary Park. He added: "There are question marks [over the mentality of players] and I don't think that's just over this period. It's something which goes beyond that. It's something I am finding out about. It's a great season for learning what we have here.

"I'm talking about players 21, 22 and under. I have to give credit to Jordan Henderson and Joe Allen, they did well. They came out with some sort of credit but there weren't too many other than that. Oldham may not have been a big enough game for one or two of them but, if they don't learn, they won't be here, it's as simple as that. The same goes for the older players too.

"The boy Smith hadn't scored a goal at home in two years and he's come up against arguably two big units we had at centre-half [Skrtel and Sebastian Coates]. A boy who has come out of university football and he looks like Didier Drogba. We have seen it before with [Aston Villa's Christian] Benteke, who after our game has disappeared. You know what you are going to get at places like Oldham. You have to roll your sleeves up and fight but we were too soft."

Skrtel is the only Liverpool defender who started against Oldham as well as December's 3-1 home defeat in the league by Villa, yet Rodgers, who dropped the Slovakia international against Norwich City last weekend, says he is not singling out the 28-year-old.

"I'm talking in general, about the physicality around the team, not just Martin Skrtel," he said. "For me the pressure starts higher up the pitch. It was too easy for the ball to be played forward. Can we stop the ball coming forwards? It was similar to the first goal at Stoke, when it was played out to Huth. We're looking for pressure at the top end of the pitch."

Rodgers rejected any suggestion that his own signings – £10.5m Fabio Borini, £15m Allen and £12m Sturridge – are not equipped to correct the lack of physicality, and leadership, that he has identified as a problem at Liverpool. He countered: "If you ask people about Borini, they'd say his biggest attribute is his physicality. His power and aggression – that's what he's renowned for. That's something he needs to improve on because that's his strength.

"As for Joe Allen, I've seen Joe throw Yaya Touré to the ground last season. He has never been found wanting physically. For some players their power and strength is in their brain. Otherwise you would have basketball players throughout your team. I don't think that as a team we are physically light or short in anyway. I think it's mental and that's something we need to improve."

Coutinho arrived on Merseyside for a medical on Monday ahead of a proposed £8.5m transfer from Internazionale. Liverpool require a work permit for the midfielder, who has been capped once at senior level by Brazil, before completing the deal.